1. Field of the Invention
This invention relates to providing protection, monitoring, and management of electric power systems, and more particularly, to the testing of relays which provide such functions without interruption of the protective functions.
2. Background Information
The electric power industry has developed sophisticated relays that perform multiple protection, monitoring and management functions for electric power systems. Such relays are very complex and now employ microprocessors to implement the numerous functions. The protection functions performed can generate trip signals which lead to interruption of current in the event that protection criteria are exceeded. Protection is typically provided for phase, ground, and negative sequence, instantaneous and time overcurrents. Under voltage, overvoltage and under frequency protection can also be provided. The monitoring functions can include waveform capture and logging of many parameters. As a result, there are numerous settings that must be loaded into the relay. These settings interact to effect the overall performance of the relay. Thus, merely confirming that the intended settings have been entered does not assure that the desired performance will be obtained.
It is known, therefore, to test the relays by inserting test values of power system currents and voltages utilized by the relay, selected to simulate a desired condition. To date, such testing has required termination of the protective functions.
There is an interest in being able to maintain the protection functions of a power system relay while performing tests.
The present invention is directed to a method of testing power system relays on-line without losing the protection functions. The on-line method of testing a power system relay that utilizes sensed values of power system current and voltage to perform specified functions comprises: substituting test values for the sensed values of power system parameters to perform the specified functions while simultaneously monitoring the sensed values of at least the power system currents. The method further includes terminating use of the test values and returning to use of the sensed values of power system parameters to perform the specified relay functions when the sensed value of at least one of the power system currents exceeds a selected threshold. This threshold can be about 10 percent of rated current. Termination of use of the test values and return to the use of the sensed values of power system current and voltage also occurs when a selected time interval after initiation of the use of the test values has expired. This selected time interval can be an interval which exceeds the time required for the relay to respond to the longest event simulated by the test values. As another aspect of the invention, the sensed values of the power system currents and voltages that result in a certain event under a specified relay function are stored and subsequently used as the test values. Such an event can include the generation of a trip signal.
The invention also encompasses an electric power system relay incorporating a simulator for testing the relay without loss of the protection functions. More particularly it relates to such a relay which includes relay logic performing specified relay functions, sensors generating sensed values of current and voltage for use by the relay logic in performing the specified relay functions, and a simulator having an input device for inputting test values of current and voltage, a data switch having a first position in which the sensed values of current and voltage are provided to the relay logic for performing the specified relay functions, and a second position in which the test values are provided to the relay logic for performing the specified relay functions in place of the sensed values of current and voltage, and switch logic monitoring the sensed values of current and voltage and operating the data switch from the second position to the first position to remove the test values of current and voltage from the relay logic and to reapply the sensed values of current and voltage to the relay logic. The switch logic further includes a timer that also operates the data switch from the second position to the first position to remove the test values of current and voltage from the relay logic and to reapply the sensed values of current and voltage to the relay logic when a selected timing interval expires. Preferably, the selected timing interval is longer than the time required for the relay logic to perform the specified relay functions. The relay logic can also include a memory in which the sensed values of current and voltage are stored for later use by the simulator as test values.